A network may configure a set of recommended cells for a user equipment (UE) in the case the UE may move among different areas. Thus, a UE may need to perform cell selection or re-selection procedures. For example, a network may configure a set of cells or areas such as radio access network (RAN) based paging area or RAN notification area for a connected UE or an inactive UE when the UE performs a cell selection or re-selection procedure due to the UE mobility. A network may also provide a set of cells that provide Multimedia Broadcast Multicast Services (MBMS) service by Single Cell Point-to-Multipoint (SC-PTM) for MBMS service continuity purposes. The recommended set of cells may include one or more sets of cells information such as RAN notification area, MBMS, SCPTM, and so forth for different purposes.
For a New Radio (NR) communication system, a service based cell re-selection procedure has been adopted. However, the exact mechanism as for how to maintain service continuities for certain services has not been determined. Also, it has been determined that a NR communication system would support inter-frequency service based cell re-selection mechanism. However, which services would apply this mechanism has not been determined. Further, in the current LTE, the service based cell re-selection could be supported by sidelink communication, V2X sidelink communication, MBMS Service, and MBMS Service via SC-PTM reception. But for the intra-frequency service based cell re-selection mechanism, it is unclear whether such service could be supported by all cells that operate at the same frequency.
If a wireless communication service could be more flexibly and effectively provided, utilization of radio resources could be increased. For instance, utilization of radio resources could be increased if the granularity of the MBMS service via SC-PTM could be per cell and not the whole SFN. Without intra-frequency service based cell re-selection, service continuities could be difficult to maintain. For instance, if a neighboring cell that could provide a wireless service is not the best cell, then service continuities might not be maintained. If an idle UE receives MBMS via SC-PTM, then the idle UE may need to return to a connected mode in order to request the wireless service. If the idle UE intends to perform (V2X) sidelink communication, then the idle UE may need to become a synchronization source. To support intra-frequency service based cell re-selection, a UE may need to prioritize some cells based on recommended information in the cell re-selection scheme.
A UE may perform a cell re-selection process by obtaining at least frequency priority information such as a re-selection priority from a network. The re-selection priority may be used to limit required measurements or to find a best cell. When a UE performs measurements because of a reselection process has been trigger due to, for example, UE mobility, the UE may follow the existing rules to limit required measurements in a LTE system.
FIG. 1 illustrates a current cell re-selection process. It is worth noting that in the current cell re-selection process, a UE may not need to prioritize some cells. High level criterions of current cell re-selection process would depend on frequency priority, radio link quality, or cell accessibility. Referring to FIG. 1, in step S101, the UE would perform a frequency priority configuration which could be used as re-selection priority for prioritizing signal measurement. In step S102, the UE would measure a signal quality of a frequency so as to measure a cell's signal quality. In step S103, the UE would attempt to find a potential best cell or candidate cell based on the measured signal quality. For example, a UE may find the best cell by measuring each cell and by determining whether the measured cell would satisfy a selection condition. For cells that would satisfy the selection condition, the cells would be ranked based on the cells' signal quality.
A UE may choose not to perform intra-frequency measurements when the serving cell's radio link quality is greater than a threshold. For an inter-frequency with a re-selection priority higher than the re-selection priority of the current frequency, the UE will perform measurements of higher priority inter-frequency. For an inter-frequency with an equal or lower re-selection priority than the re-selection priority of the current frequency, if the serving cell's radio link quality is greater than a threshold, the UE may choose not to perform measurements of the inter-frequencies. For each measured cell, the UE may calculate a criterion S value based on the measured signal quality. If a measured cell's criterion S value has fulfilled a re-selection condition, the UE would further calculate a criterion R value for the cell. For example, the selection condition may be the criterion S value>0. After the measurement, the UE may get a list of cells that fulfill the selection condition. After step S103, the UE would then choose a cell with the biggest criterion R value, operates at the highest re-selection priority frequency, and is not marked as restricted or barred as a best cell.
In step S104, the UE would check whether the best cell that has been determined is restricted or barred. For the best cell, the UE may check whether the best cell is restricted or barred by reading the system information. Once the best cell is restricted or barred, the UE will mark the cell as restricted or barred and re-find a best cell. The status of the best cell with regard to whether the cell has been restricted or barred can be located in system information which has been broadcasted or transmitted. If the status of the best cell is ‘not barred’ and ‘not reserved’, then this cell would be treated as a candidate cell. For this step, the UE would need to read the system information block (SIB) within the system information. In step S105, if the best cell has been marked as ‘barred’ and ‘reserved’, then the best cell would not be regarded as a candidate cell, and step S104 would be repeated.
Next, in step S106, the UE would check whether the candidate cell would satisfy the re-selection conditions. If the best cell is not restricted or barred after checking system information, the best cell will be treated as a candidate cell. When the UE finds the candidate cell, the UE would verify whether the re-selection conditions have been fulfilled. The re-selection conditions which may include whether the candidate cell is better ranked than the current serving cell during a time interval and whether more than one second has elapsed after the UE has camped on the current serving cell. If the re-selection conditions have been satisfied, then the UE would continue in step S107 by connecting to the candidate cell. If no best cell was found, the UE would repeat step S102 and continue to perform measurements accordingly.
It should be noted that the NR, the cell re-selection mechanism could be refined. It could be seen from FIG. 1 and its corresponding description that the re-selection scheme does not include prioritizing certain cells based on recommended information.